The present invention relates to a machine for abrading parallel opposite, planar faces of workpieces or parts generally having a limited thickness, and which are carried by holders fitted to the workpieces, an array of the holders being configured as satellites. The invention also relates to a device for coupling electric current and transmitting fluid between a rotary structure and a non-rotary structure, as is found in the machine.
This machine can in particular be a grinding or polishing machine which atains very high precision parts by machining the planar, opposite faces thereof with the aid of an abrasive suspended in a liquid.
In machines of this type, the abrasive is introduced between the faces to be machined and the facing grinding plates, usually having a common vertical axis and which are independently rotated in the same or opposite directions. The parts to be machined, which are generally in the form of disks, are placed in off-centred recesses formed in the support satellites and have a thickness less than that of the parts to be machined. These satellites are placed between the facing faces of the grinding plates an in off-centred manner with respect to the axis thereof. On their periphery the plates are provided with teeth, which simultaneously mesh on a generally fixed external gear and on a central rotary gear. Each satellite is consequently rotated between the plates, so that each of the workpieces is subject to a cycloidal movement, independently of the movement of the grinding plates.
The combination of the movements of the satellites with those of the plates has the effect of ensuring a maximum uniformity in the machining of the workpieces with the aid of the abrasive placed between each of the plates and the corresponding face of the parts to be machined.
In grinding machines, the action of the abrasive is essentially mechanical. However, in polishing machines, the actual abrasive action can be combined with a chemical action of a liquid in which the abrasive is suspended. It should be noted that the invention is applicable both to grinding and polishing machines.
At present there are a number of grinding/polishing machines using a free abrasive operating according to the principle briefly described hereinbefore.
Thus, the SPEED FAM (U.S. manufacture) and the FUJICOSHI market grinders (Japanese manufacture) are characterized by rotations of the upper plate, lower plate and central gear which are controlled by motors positioned in the lower part of the machine. Moreover, the British LAPMASTER, the German PETER WALTERS and the Italian MELCHIORRE polishing machines, are characterized by rotation of the upper plate which is controlled by a motor located in the machine head.
In all these known machines, there are sensitive parts requiring relatively frequent maintenance are deeply enbedded within the mechanical structure of the machine. Thus, any intervention requires long and costly immobilization of the machine.
In addition, existing machines have all been designed with a view to the machining of mechanical parts in the workshop. They are not suitable for special requirements imposed by industries needing maximum cleanness and maximum machining accuracy (electronics, optics, etc.). Thus, in the case of monocrystalline parts intended for epitaxy in the semiconductor industry, the machining quality is not linked solely with the visible surface, but also takes account of the underlying layer in the integrity of its crystalline structure. Moreover, the parts to be machined are generally thin films or plates having a thickness below 1 mm, having a large surface (diameter often larger than 8 cm) and made from fragile materials such as glass or crystals. In order to carry out a machining of this type, it is therefore necessary to eliminate any pollution, maintain the parts clean throughout their presence in the machine, and check the characteristic quantities of the machinining (temperature, thickness of parts, pressure applied thereto, torque on the plates, etc.). Bearing in mind the overlaying structure of existing machines, it is not possible to adapt them to such cleannes conditions or to give them advanced instrumentation without calling into question the overall design of the machine.
Another problem encountered in grinding and polishing machines is due to the tendency of the parts to adhere to the plates as a result of the viscosity of the abrasive suspension. Thus, the parts have a tendency to remain stuck to the upper plate during the opening of the machine after machining. This phenomenon often leads to a fracture of the machined parts, the opening of the machine leading to the dropping of the parts on to the lower plate. None of the existing machines proposes a solution to this problem, so that the risk of parts breaking is largely dependent on precautions taken by the user.
The present invention relates to a grinding/polishing machine using a free abrasive of two parallel, opposite faces of workpieces having any desired thickness, and which machine does not suffer from the disadvantages of the prior art machines of this type. In particular, the machine according to the invention is designed in a novel manner making it possible to separate and render accessible each functional module independently of the other modules. This concept makes it possible to considerably simplify the maintenance procedures of the different modules and adapt the machine to any special machining situation which is desired to carry out. In particular, the novel design of the machine according to the invention makes it possible to supply one or more supplementary fluids to the grinding plates which, in particular, are used for maintaining an adequate cleanness while the workpiece remain in the machine. This design also makes it possible to add to the conventional instrumentation of existing machines supplementary detectors making it possible to check the machining conditions and the geometry of the machined parts.